U.S. patent application number 10/026353 was filed with the patent office on 2003-06-26 for method for encoding/decoding a binary signal state in a fault tolerant environment.
Invention is credited to Moller, Hanan Z., Sonnier, David P..
Application Number | 20030120966 10/026353 |
Document ID | / |
Family ID | 21831327 |
Filed Date | 2003-06-26 |
United States Patent
Application |
20030120966 |
Kind Code |
A1 |
Moller, Hanan Z. ; et
al. |
June 26, 2003 |
Method for encoding/decoding a binary signal state in a fault
tolerant environment
Abstract
A method for use in a fault tolerant environment for assuring
that devices within the environment switch between primary and
back-up systems in response to remotely generated control signals.
In one embodiment, the inventive system uses a binary code in the
form of a pair of different frequency signals, i.e., a binary zero
is represented by one frequency and a binary one is represented by
another frequency. The signals may be continuous or may be sent in
timed bursts. At the individual devices, such as the aforementioned
line cards, a receiver is provided to detect the presence of the
signals. Since the line cards already have receivers to detect the
binary signal, modification to detect a frequency signal requires
the addition of minimal components. The receiver also includes
circuitry for reporting the status of the card and such circuitry
can be used to report to the remote controller whether the signals
are reaching the line card. Alternately, the signals could be sent
in burst format using a single frequency in which the number of
bursts could indicate a binary one or a binary zero. For example,
if N bursts are received in some unit of time, that could be
indicative of one binary state. If 2N burst are received in the
same unit of time, that could be indicative of another binary
state. In another form, the receiver could be programmed to look
for N changes of frequency per unit of time to indicate one binary
state and 2N changes of frequency could be indicative of another
binary state.
Inventors: |
Moller, Hanan Z.; (Austin,
TX) ; Sonnier, David P.; (Austin, TX) |
Correspondence
Address: |
BEUSSE, BROWNLEE, BOWDOIN & WOLTER, P. A.
390 NORTH ORANGE AVENUE
SUITE 2500
ORLANDO
FL
32801
US
|
Family ID: |
21831327 |
Appl. No.: |
10/026353 |
Filed: |
December 21, 2001 |
Current U.S.
Class: |
714/2 ;
382/165 |
Current CPC
Class: |
H04L 43/0817 20130101;
H04L 41/0663 20130101 |
Class at
Publication: |
714/2 ;
382/165 |
International
Class: |
G06K 009/00 |
Claims
What is claimed is:
1. In a fault tolerant system having a primary device and at least
one redundant device, and further having a remote controller for
monitoring the status of the devices and providing a control signal
to switch from the primary device to the redundant device upon
detection of a failure in the primary device, a method of
determining validity of the control signal comprising: continually
sending a first signal having a predetermined varying
characteristic to at least the primary device from the remote
controller; and sending a second signal having a different varying
characteristic to at least the primary device from the remote
controller upon detection of a failure of the primary device.
2. The method of claim 1 wherein the varying characteristic
comprises a signal frequency.
3. The method of claim 2 wherein the signal frequency is a
continuous wave frequency.
4. The method of claim 2 wherein the signal frequency is a selected
number of signals per unit of time.
5. The method of claim 1 wherein the at least one device includes a
receiver responsive to the to the first signal for acknowledging
receipt thereof to the remote controller.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to fault tolerant systems and,
more particularly, to a method for confirming validity of a control
signal for energizing a back-up system in a fault tolerant
environment.
[0002] Numerous electronic control systems utilize multiple
redundant systems to assure fault tolerance in critical
applications. One example of such a system is a redundant switching
fabric for a communication line card installation. Typically, such
systems have two switching fabrics, a primary and a back-up. All of
the line cards are connected to the outside world through the
switching fabric. In the event that the primary fabric has a
failure, the system has to switch to the backup fabric. In this
example, the switching function resides on each line card and a
remote controller provides a binary state signal to each card to
let the card know when to switch to the back-up fabric.
[0003] One potential problem with such systems is that the control
signal may become tied to one of the binary states and be unable to
switch in response to the remote controller. For example, if a
binary zero is used to maintain the line cards connected to the
primary fabric and the control signal line becomes grounded, the
line card will not receive a binary one signal generated by the
controller when the binary one signal is used to command a change
to the backup fabric. Another potential problem is that the control
signal could fail into the switch state and cause one or more of
the components to switch in error. In particular, a subset of the
components might see the switch indication. This is particularly
undesirable since it could lead to a partitioning of the system and
result in a system failure. This type failure is not amenable to
the test mode described below. There are solutions to this problem
as well, such as running dual redundant signals and then running
tests on both of them but such additional redundancy introduces
more complexity. One solution to this problem is to periodically
run a test mode in which a test signal is sent to each line card
and a check is then made to determine if the line card responded to
the test signal. While this approach may be suitable in simple
systems having only a few devices that need to switch, verifying
that each line card in a typical communication system has switched
presents a complex problem. Accordingly, it would be desirable to
provide a method for continually verifying proper operation of
devices in response to control signals in a fault tolerant
environment.
SUMMARY OF THE INVENTION
[0004] The present invention is directed to a method for use in a
fault tolerant environment for assuring that devices within the
environment switch between primary and back-up systems in response
to remotely generated control signals. In one embodiment, the
inventive system uses a binary code in the form of a pair of
different frequency signals, i.e., a binary zero is represented by
one frequency and a binary one is represented by another frequency.
The signals may be continuous or may be sent in timed bursts. At
the individual devices, such as the aforementioned line cards, a
receiver is provided to detect the presence of the signals. Since
the line cards already have receivers to detect the binary signal,
modification to detect a frequency signal requires the addition of
minimal components. The receiver also includes circuitry for
reporting the status of the card and such circuitry can be used to
report to the remote controller whether the signals are reaching
the line card. Alternately, the signals could be sent in burst
format using a single frequency in which the number of bursts could
indicate a binary one or a binary zero. For example, if N bursts
are received in some unit of time, that could be indicative of one
binary state. If 2N burst are received in the same unit of time,
that could be indicative of another binary state. In another form,
the receiver could be programmed to look for N changes of frequency
per unit of time to indicate one binary state and 2N changes of
frequency could be indicative of another binary state. In any of
the examples, the receiver could be programmed to notify the remote
controller whenever signals are being received and the absence of
signal confirmation at the controller would be indicative of a loss
of the control signal. In this way, the system would always know
whether or not the control signal is being transmitted to the
devices and thereby provide assurance that the redundancy is
available.
BRIEF DESCRIPTION OF THE DRAWING
[0005] For a better understanding of the present invention
reference may be had to the following detailed description taken in
conjunction with the accompanying drawing in which:
[0006] FIG. 1 is a simplified illustration of a phone switching
system incorporating a redundant switching fabric with which the
present invention may be used; and
[0007] FIG. 2 is a graph illustrating two forms of control
signals.
DETAILED DESCRIPTION OF THE INVENTION
[0008] Referring to FIG. 1, there is illustrated a portion of a
communication switching system 10 with which the present invention
may be used. The system includes a block 12 identified as a remote
controller which monitors and directs data flow into a distribution
network. Data entering block 12 at line 14 is directed into a data
distribution block 16 which forwards the data into multiple
selected paths, two of which are shown at 18 and 20 coupling the
data into a pair of redundant switching fabrics 22 and 24. The
switching fabrics couple data signals to and from a set of line
cards 26. In the communication system, the line cards are arranged
so that each card directs calls to a specific communication line.
The switching fabric is essentially a back plane connecting the
line cards to the communication lines. In existing systems, the
remote controller monitors operation of the switching fabric and
determines whether there is any failure in the fabric. In the event
of a failure, the controller 12 provides a DC signal to instruct
the line cards to switch their respective inputs and outputs to the
back-up fabric. Both the switching fabrics 22 and 24 are arranged
to couple output data through a data select block 28. The block 28
functions to pass data from either fabric to an output bus 30.
[0009] In prior art systems, the controller 12 uses a bi-level
control signal on a control voltage line to indicate to the line
cards 26 which of the fabrics 22 and 24 are to be used to couple
data into and out of the system. For example, a signal of zero
volts would indicate use of one fabric and a signal of some
positive or negative voltage would indicate use of the other of the
fabrics. One problem with this system is that a grounded or open
control voltage line corresponds to one state of the bi-level
control signal. If the controller 12 changes the state of the
control signal, the grounded or open control line will prevent the
control signal from changing state at the line cards and thus
prevent the redundant or back-up fabric from being brought into
use, or alternately causing one or more of the line cards to switch
states in error, leading to a partitioned system.
[0010] The present invention overcomes the above described problem
with the control line signaling by changing the format of the
control signal. The bi-level control signal is replaced with a
signal that has a varying characteristic. By way of example, the
control signal may be a dual frequency signal such that a first
frequency of the signal indicates selection of a primary fabric (or
other device) and a second frequency of the signal indicates
selection of a back-up fabric (or other device). FIG. 2 at 32 shows
a first frequency at A and a second frequency at B. As another
example, the signal could be a multipulse signal in which a first
number of pulses per unit of time would indicate selection of a
first device and a second number of pulses per unit of time would
indicate selection of a second device. FIG. 2 at 34 indicates one
form of such pulsing. Other variations of this concept could be
implemented with the basic theme of a variation in the control
signal per unit time being such as to assure that a loss of control
signal can be recognized. All of these signals are characterized by
having a varying value rather than being set at some fixed value
that could be duplicated by inadvertent coupling of the control
line to some fixed value.
[0011] In the illustrative example, the line cards 26 could be
modified to receive the varying signal and provide a response to
the controller 12 confirming receipt of the signal. In one form,
the control voltage line, such as the lines 32 and 34, could be
bi-directional signal lines passing through the fabrics 22 and 24
to the respective line cards 26. Each line card could be modified
to return a recognizable signal to the controller to indicate to
the controller that the control voltage signal was received.
Various types of signal responsive circuits are known in the art
for performing this function. Further, while the control signal
line is shown as a hard-wired line in the drawing, it will be
understood that the return signal could be a wireless
transmission.
[0012] While the invention has been described in what is presently
considered to be a preferred embodiment, various modifications will
become apparent to those skilled in the art. It is intended
therefore that the invention not be limited to the specific
disclosed embodiment but be interpreted within the full spirit and
scope of the appended claims.
* * * * *